System And Method Of Forming Variable Density Seating Materials

ABSTRACT

A system and method of forming seating materials having variable density gradient for high hardness ratio of high-to-low deflection, and more specifically to forming foam materials for vehicle seats having variable density gradient that allow greater comfort across a wider range of occupant weights.

CROSS REFERENCE TO RELATED APPLICATION

This U.S. National Stage Patent Application claims the benefit of International Application serial number PCT/US11/43825 filed Jul. 13, 2011, entitled “System And Method Of Forming Variable Density Seating Materials” and U.S. Provisional Patent Application Serial No. 61/363,820 filed Jul. 13, 2010, entitled “System And Method Of Forming Variable Density Seating Materials,” the entire disclosures of the applications being considered part of the disclosure of this application, and hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention generally relates to a system and method of forming seating materials having a variable density gradient and more specifically to forming foam materials for vehicle seats having a variable density gradient that allow greater comfort across a wider range of occupant weights, and the use of single foam formulations across a wide range of types of vehicle seats having significantly different desired performance characteristics.

2. Related Art

Vehicle manufacturers must make their vehicle seats comfortable to a wide range of vehicle occupants having significantly different weights and sizes. The manufacturer of a vehicle seat must consider a weight range from that of a small child who no longer needs a booster seat through the upper weight and size range of adults. A lighter occupant and a heavier occupant would find the same vehicle seat to perform significantly different, and each occupant would prefer very different hardness and more specifically the amount of deflection of seating materials. For example, the static comfort of a seating foam, such as a polyurethane seating foam, depends greatly on the hardness and density of the foam, especially at high deflection. Although vehicle manufacturers attempt to select the hardness of the foam to provide desired static comfort for a wide range of occupant weights, it is difficult to please every occupant due to the variation between occupant weights and thereby the amount of deflection which is related to the occupant's penetration into the foam while sitting upon the seat. More specifically, a soft foam material is likely to provide a comfortable seat for a light occupant, while most heavy occupants would feel bottomed out, feel frame components, or feel uncomfortable in the same seat. Conversely, a harder foam generally ensures a comfortable seating material for a heavy occupant, but also results in less deflection, which causes lighter occupants to find the seat not comfortable, such as the seat being too hard, causing them to sit on top of the foam, and not sink, at least partially, into the foam. While manufacturers may adjust the hardness of the foam to that preferred by an average user, the more displaced the vehicle occupant is in weight from the average user, the less comfortable they find the vehicle seat. Therefore, in a single material, a single piece of foam construction seat, to date manufactures are limited in their ability to provide a comfortable seating surface for a wide range of occupant weights.

The variance in comfort of seating materials or desired performance of seating materials may also vary depending on the desired application, vehicle type, target consumer, and vehicle manufacturer preferences. For example, in many sport or performance cars, it is desirable to have a firmer seat than in luxury cars.

Originally, to address the desire for different seating characteristics, and in particular the hardness of the foam, most manufacturers created a wide variety of foam formulations. While these different foam formulations allowed variations in the properties of the particular seat to be addressed, it did not solve any of the above described problems related to the differences between occupants of the vehicle seats. In addition, the demand for increased comfort and increased durability, as well as an expanded range of required properties, limit the ability of manufacturers to address all desired properties with only changing the foam formulation. Furthermore, as the range of required properties increase and the desire of high hardness foam for some individuals and low hardness foam for comfort for other individuals, these competing dynamic comfort issues caused the foam formulations used to not be as well-balanced chemical mixes as traditional foam formulations and therefore caused difficulty during the manufacturing process. Also, many of these unique foam formulations required specialty chemicals which increased raw material costs and at times required additional manufacturing equipment and processes which increased the cost of the vehicle seat.

To address the above shortcomings and a wider weight range of vehicle occupants, some manufacturers have created a two-part foam assembly for the seating material, which requires time consuming and expensive manufacturing processes. Therefore, due to the cost of assembly of multiple slabs of foam having different densities, its application across a wide range of vehicle seats is currently limited. The two-part seat material may be formed by two methods. The first is to generally apply a separately soft layer of foam to a harder molded foam wherein the soft slab of foam is closest to the A surface or seating surface of the seat material. In such a method of forming a two-part foam seating material, first the harder foam seat material is molded and then a second softer seat material is molded or cut from slabstock foam with the desired shape. Then, the two parts are glued together with an adhesive, which increases production costs significantly due to the extra labor, equipment, materials and space needed. As manufactures also strive to improve the environmental aspects of the manufacturing process as well as the recyclability of the materials, the use of an adhesive to glue the soft die cut slabstock foam or separately molded piece to the harder molded foam is generally not desirable. For example, in using the two-part seating material, the adhesive may make it more difficult to recycle the seat at the end of the life cycle and it is difficult to find environmentally friendly adhesives with desired performance characteristics over the life cycle of the seat.

The second method some seating manufacturers have also developed is a mold-in process to form a two-part seating material that eliminates the need for the adhesive. Even though the need for the adhesive is eliminated, significant disadvantages also occur in the molding process that significantly slow the line speed and processing time for each seating material. More specifically, many manufacturers use a method of foam production that pours multiple formulations within one mold, typically in layers to achieve high hardness bolsters while maintaining a softer insert near the A surface. The additional formulations and processing steps require additional space to store the different components that are used in the mold, additional equipment space, and additional demands are placed on the operators of the manufacturing process. Furthermore, no suitable technology has been found to date to prevent contamination of the mold-in slab from the liquid polyurethane chemical blends mixing during foaming process. More specifically, many times the different layers of foam would have uncontrollable or undesirable blending or be outside of their desired layer boundaries such as a hard foam formulation intruding upon an area where a soft foam formulation is desired and even worse, at times intruding only partially, causing an uneven feeling of hardness or hard spots in the vehicle seat. Though many manufacturers adjusted the pour processes to attempt to prevent such quality issues, this often added complexity, and cost in the manufacturing process and also limited at times the types of formulations that may be used with each other. This contamination or mixing of formulations typically negates the comfort benefit found in providing a slab-molded two-part material seating slab.

In vehicle seats that used a backing material such as placing a precut cloth-like material in the mold and then directly molding foam to the material other problems may occur. These methods are typically used to produce a strong B surface bond for increased durability as well as other performance characteristics but are difficult to use with multiple foam formulations as well as the above described two-part mold in process. More specifically, molding to a backing material in the mold may create a number of issues during the foam molding process, such as movement of the backing material as multiple layers are injected, as well as the undesirable mixing of various types of materials.

SUMMARY

The present invention generally relates to a system and method of forming seating materials having variable density gradient for high hardness ratio of high-to-low deflection. More specifically to forming foam materials for vehicle seats having variable density gradient that allow greater comfort across a wider range of occupant weights.

The present invention uses a method to create a variable hardness seating material with only minimal tooling changes and limited to no reduction in manufacturing efficiency. First, the material is placed in a mold and then expanded to fill the mold. Unlike prior molds, the present invention uses molds that have larger cavity areas in which moveable plates or mold sections rest. With the mold cavities filled with the expanded foam and approaching the cured state, the moveable plate compresses the seat to the final size, such that the areas closest to the moveable plate are compressed to have greater densities. This creates a variable density seat with greater differential in hardness between low and high deflections. The seat foam is more comfortable to a wide range of occupant weights, deflecting as desired for the lighter weight occupants while providing sufficient support for heavier occupants in order to prevent the sensation known as “bottoming out.”

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the systems and methods according to the present disclosure will be described in detail, with reference to the following figures, wherein:

FIG. 1 illustrates an exemplary seating mold with an A surface being on the bottom side and the initial location of the mold materials after the mold of the present invention is closed;

FIG. 2 illustrates the mold in FIG. 1 with the foam seating material expanded to completely fill the mold cavity and a moveable plate in a first position;

FIG. 3 illustrates the mold of FIG. 2 wherein the moveable plate has moved from the first position to a second position, which compresses the seating material providing the illustrated increased density gradient on the backside of the seating material;

FIG. 4 illustrates an exemplary graph of strain in millimeters relative to an applied force to the seating material of the present invention compared to that of a conventional seating material;

FIG. 5 illustrates an exemplary graph of frequency versus transmissibility using the same formulation, density and thickness wherein transmissibility has the same formulation density and thickness;

FIG. 6 illustrates deflection versus hardness with the same formulation, thickness and weight; and

FIG. 7 illustrates an exemplary graph of a load deflection curve with the deflector percentage versus force and more specifically illustrating that a similar load deflection curve may be obtained using a foam that is only 70 mm and 1,096 g versus conventional foam that is 96 mm and 1,220 g.

DETAILED DESCRIPTION

The present invention generally relates to a system and method of forming a seat (not illustrated). The seat generally includes a seating material that provides support to the vehicle occupant, such as the illustrated foam base 10. The foam base 10 includes an A surface 12, a back surface 13 and bolsters 18. As further illustrated in FIG. 3, the cross sectional view shows a density gradient area 14, having a higher density area 15 and a lower density area 16 in the final foam base 10 configuration.

The seat, specifically the foam base 10, is generally formed in a mold. While the seat material, in particular the foam base 10, may be formed in any style, size, or configuration, the Figures show an exemplary seat and the present invention is applicable to other styles and configurations. In addition, the mold 20 would vary in style, shape, size, and configuration as desired to form the particular desired seating material and in addition to the illustrated foam base 10. The mold 20 generally includes a base 24 and sidewalls 26 into which the foam material is placed for the mold process to begin. The illustrated mold 20 generally includes bolster cavities 28 and a main cavity 30 which are confined by the sidewalls 26, base 24, and an upper plate 32. As illustrated in FIG. 2, the upper plate 32 may have a first or retracted position 34, and as further illustrated in FIG. 3, a second or extended position 36. The illustrated mold 20 is for forming a base 10 of a seat and different molds may be used for different styles, shapes, sizes and configurations, as well as different molds to be required for the seating materials for the upper back of a seat, or for example, a rear seat of a vehicle. In addition, even though not illustrated, other portions of the mold may include additional moveable plates to vary the density of other portions of the seat such as a moveable plate in the bolster area (not illustrated) to provide different densities in the bolster area.

The present invention, and in particular the process of forming the seat, starts similar to other seat forming processes in that the mold is open and a mold material such as a polyurethane seating foam initial material is placed or inserted in the mold in desired quantities and then the mold is closed. The mold, depending upon the type of material used, may be preheated to a desired temperature before the material is placed into the mold. The material 11 may be any type of material commonly used or desirable for use in forming the seating structure. The present invention as illustrated in FIG. 4 compares a conventional polyurethane foam seat base to a polyurethane foam seat base that incorporates the present invention. With the polyurethane foam material 11 being placed in the mold in the desired quantities, the process of expanding the foam to fill the mold starts as illustrated in FIG. 2. More specifically, the material in FIG. 2 has filled the mold and has reached a state of semi-cure and normally would be allowed to stay in the mold without change for some additional specified time period. The mold 20 of the present invention includes an enlarged cavity area such as the illustrated main cavity 30 wherein in the initial position as illustrated in FIG. 2 the foam fills a greater area than desired for the final seat base 10 as illustrated in FIG. 3. Once the mold material has completely filled the mold cavity 30 for the desired time, the inner plate 32 is moved from the first position 34 as illustrated in FIG. 2 to the second position 36 as illustrated in FIG. 3. Upon the movement of the upper plate 32 to the second position 36, the mold cavity forms the final desired shape and size of the seat base 10. As illustrated in FIG. 3, by moving the upper plate 32 from the first position 34 to the second position 36, the area closest to the upper plate 32 of the foam base 10 has the highest density area 15. In comparison, the lowest density area 16 is furthest away from the upper plate 32 and is approximately the A surface 12 which is engaged against the A mold surface 24. The density of the foam in the main cavity 30 may vary on a gradual even density gradient but is expected that the increase in density is more of an exponential nature than a linear nature. More specifically, the lower density area 16 extends further into the foam base 10 and as it approaches the back surface 13, the density substantially increases quickly to the high density area 15. As the graph illustrates in FIG. 4, the present invention allows for low hardness at low deflection and then increased hardness at a higher rate than a conventional seat foam as the deflection increases. The present invention as illustrated in FIG. 4 provides a better static comfort for a wider range of occupant weights while eliminating expensive two-part foam seating materials. Furthermore, the present invention may use less material and have less overall mass by providing high density in only the sections where needed.

The mold 20 is only one style of a particular foam base 10, and other styles may be used which in addition include other areas that include moveable plates in addition to the illustrated upper plate or in place of the upper plate, such that the density gradient could have greater adjustment to particular seat styles, shapes or configurations allowing for the complete tailoring of a particular seat for the most comfortable possible position. For example, the cavity of the bolster cavity 28 could be intentionally enlarged and include a moveable bolster plate (not illustrated) that increases the density on the outer boundaries of the bolsters to provide more support when needed.

In addition, for molds such as those that form the upper back of the seating material to provide comfort along the complete upper back, the moveable plate may not have uniform compression along the length of the upper back (not illustrated). Therefore, it is possible through using multiple plates across a surface to create various density gradients where desired to increase seating comfort. Another example, though not illustrated for a seating base such as the illustrated foam base 10, would be to provide a larger cavity near the rear surface of the seat than the front edge of the seat and then compresses such that the density gradient also varies between the rear of the foam base to the front of the foam base. The front, where less weight is placed by the legs, would have a softer, more comfortable seating position, while the seat would allow greater support in the foam base where the most weight is placed by a particular user. This would increase seating comfort and reduce fatigue of the vehicle operator.

It is important to note in FIG. 7 that both the mass and thickness provide a reduction in vehicle weight and also provides increased cabin space.

The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. 

In the claims:
 1. A method of forming a seat cushion comprising: providing an uncured foam material; providing a mold having at least two mold members which cooperate to form a mold cavity and wherein one of said at least two mold members includes at least one moveable member capable of extending from a retracted position to and extended position within said mold cavity and wherein said moveable member decreases the volume of said mold cavity in said extended position; inserting said uncured foam material within said mold cavity; allowing said uncured foam material to partially cure to an intermediate state; moving said at least one moveable member to said extended position and wherein in said extended position a mold surface of said moveable member engages said uncured foam material in said intermediate state; allowing said uncured foam material in said intermediate state to cure to a final state; and removing the seat cushion formed from said foam material in a final state.
 2. The method of claim 1 wherein said step of moving said at least one moveable member includes the step of creating a density gradient in said uncured foam in said intermediate state.
 3. The method of claim 1 wherein said step of providing an uncured foam material further includes the steps of inserting said uncured foam material into a portion of the mold cavity defined by one of said mold members and closing the mold halves to create said mold cavity including said uncured foam material.
 4. The method of claim 3 wherein said step of inserting said uncured foam material into a portion of the mold cavity further includes the step of inserting the providing a substantially homogenous foam material.
 5. The method of claim 1 wherein at least one of said mold members does not include a moveable member and wherein said step of inserting said uncured foam material further includes the step of inserting the uncured foam material into said mold member without said moveable member.
 6. The method of claim 1 wherein said moveable member in said retracted position does not engage said uncured foam material.
 7. The method of claim 1 wherein said step of allowing said uncured foam material to partially cure to an intermediate state further includes the step of applying heat for a specified amount of time.
 8. The method of claim 1 wherein said step of allowing said uncured foam material to partially cure further includes the step of allowing said uncured foam material to expand to at least contact said moveable member in said intermediate state and wherein said uncured foam material when initially placed in said mold member does not touch said moveable member.
 9. The method of claim 1 wherein said step of moving said at least one moveable further includes the step of creating a density gradient in said foam material.
 10. The method of claim 1 wherein said step of allowing said uncured foam material in said intermediate state to cure to a final state further includes the step of maintaining said moveable member in said extended state.
 11. The method of claim 1 wherein said step of allowing said uncured foam material in said intermediate state to cure to a final state further includes the step of retracting said moveable member to a position between said extended state and said retracted state.
 12. The method of claim 1 wherein said step of allowing said uncured foam to partially cure includes the step of allowing said uncured foam to substantially fill said mold cavity.
 13. The method of claim 12 wherein said step of moving said at least one moveable member to said extended position and wherein in said extended position a mold surface of said moveable member engages said uncured foam material in said intermediate state, includes the step of reducing the volume of said mold cavity as said at least one moveable member moves to said extended position and wherein the seat cushion has a volume substantially equal to the reduced volume mold cavity.
 14. A seat cushion comprising: a foam material having an outer surface include a first surface and an opposing second surface and wherein said foam has a variable density gradient between said first surface and said second surface and wherein said foam material has a density that is greater at said second surface than at said first surface and wherein said seat cushion is formed by a process comprising: providing an uncured foam material; providing a mold having at least two mold members which cooperate to form a mold cavity and wherein one of said at least two mold members includes at least one moveable member capable of extending from a retracted position to and extended position within said mold cavity and wherein said moveable member decreases the volume of said mold cavity in said extended position; inserting said uncured foam material within said mold cavity; allowing said uncured foam material to partially cure to an intermediate state; moving said at least one moveable member to said extended position and wherein in said extended position a mold surface of said moveable member engages said uncured foam material in said intermediate state; allowing said uncured foam material in said intermediate state to cure to a final state; and removing the seat cushion formed from said foam material in a final state.
 15. The seat cushion of claim 12 wherein said density gradient varies exponentially between said first surface and said second surface. 